A chimeric antigen receptor (hereinafter, also referred to as “CAR”) is an artificial chimeric protein in which a single chain antibody that recognizes a cell surface antigen on a cancer cell is fused with a signal transduction region that induces the activation of a T cell. As shown in FIG. 1, the transfer of a gene encoding CAR to a non-tumor-reactive normal peripheral blood T cell (peripheral blood T lymphocyte) enables the large-scale preparation of a CAR-expressing T cell (hereinafter, also simply referred to as “CAR-T cell”) that are capable of expressing CAR. The CAR-T cell is tumor-reactive and can cause damage to a cancer cell without depending on interaction with a major histocompatibility complex (MHC).
Cancer immunotherapy by the administration of the CAR-T cells, more specifically, therapy which involves collecting T cells from a patient, transferring a gene encoding CAR to the T cells, and transferring the T cells again to the patient (see non-patent document 1) is currently under clinical trial around the world and has yielded results that indicate effectiveness for, for example, malignant tumor in the hematopoietic organ, such as leukemia or lymphoma.
In recent years, research has been made on various CAR-T cells. There have been proposed, for example, a pharmaceutical composition comprising modified autologous human T cells comprising a nucleic acid encoding CAR consisting of a CD19 antigen-binding region, a transmembrane region, a 4-1BB costimulatory signal region, and a CD3ζ signal region (see patent document 1), one or more therapeutically effective anti-tag chimeric antigen receptor (AT-CAR)-expressing T cell populations which are administered to a subject concurrently with or separately from a formulation of one or more tagged proteins binding to cancer cells, wherein the AT-CAR-expressing T cell populations bind to the tagged proteins and induce cancer cell death (see patent document 2), cells comprising a nucleic acid encoding a chimeric antigen receptor comprising an antigen-binding domain of human antibody 139, an extracellular hinge domain, a transmembrane domain, and an intracellular T cell signal transduction domain (see patent document 3), cells comprising a nucleic acid sequence encoding a chimeric antigen receptor, wherein the chimeric antigen receptor comprises a CD3ζ signal transduction domain comprising an antigen-binding domain, a transmembrane domain, a costimulatory signal transduction region, and the amino acid sequence of SEQ ID NO:24 (see patent document 4), genetically engineered CD19-specific T cells which express and retain a CD19-specific chimeric receptor on their cell surface membranes, wherein the chimeric receptor consists of an intracellular signaling domain for immunocyte effector functions, at least one transmembrane domain, and at least one extracellular domain, and the extracellular domain comprises a CD19-specific receptor (see patent document 5), and chimeric antigen receptor-expressing cells harboring a nucleic acid encoding a chimeric antigen receptor comprising, as an intracellular domain, an intracellular domain of a glucocorticoid-induced tumor necrosis factor receptor (GITR) (see patent document 6).
However, none of the previous techniques have solved the problem of low survival efficiency of CAR-T cells in vivo or insufficient activation of endogenous T cells induced by CAR-T cells or insufficient local accumulation thereof to tumor, or the problems of immunosuppressive signals mediated by the PD-L1/PD-1 pathway which is the tumor immune escape mechanism of cancer cells, and the inhibition of the activity of CAR-T cells by immunosuppressive factors such as TGF-β or IL-10 secreted in a cancer microenvironment. Therefore, there exist cancer types or cases on which no sufficient therapeutic effect is confirmed. Thus, it has been desired to prepare more effective CAR-T cells, and an expression vector for the preparation of the CAR-T cells.